This invention relates to stencilling apparatus, and more particularly, to screen stencil printing with a recycled stencil fluid, the viscosity of which is regulated in response to sensing thereof by the flow coater.
Screen stencilling is widely used for selectively depositing coating materials such as inks, adhesives, and other functional and/or decorative deposits through a screen stencil onto stock such as paper, polymers, cloth, wood, laminates, and the like for making posters, decalcomania coatings, graphic designs, and the like. A typical apparatus for screen stencilling is set forth in U.S. Pat. No. 2,606,492. Usually, the process involves the spreading of a layer of the fluid on a fine mesh screen, followed by forcing a part of the fluid layer through the pattern areas of the screen with a squeegee onto the stock. The excess ink is forced to one end of the screen by this squeegee. The excess ink is spread back into the screen by a flow coater for the next stencilling stroke. A common tendency of the stencilling fluid is to thicken because of solvent or carrier liquid evaporation while the stencilling fluid is repeatedly spread on the stencil screen.
One type of apparatus for controlling the viscosity of the stencilling fluid is set forth in U.S. Pat. No. 3,252,411. In such apparatus, the fluid is pumped out of the printing apparatus to special external viscosity testing and altering equipment associated with the printing carriage. The fluid is then pumped back to the ink reservoir for application to the stencil screen. This last-noted apparatus does provide viscosity control not achievable with the prior equipment. However, the apparatus is relatively complex, especially with regard to the separated viscosity testing and altering equipment.